Poweb-cqntkol apparatus fob pneumatic-dispatch systems



' r 1,625,903 April 26,1927. J. G MACLAREN POWER CONTROL APPARATUS FOR PNEUMATIC DISPATCH SYSTEIS Filed May 12. 1926 3 Sheets-Sheet 1 4y Qua- 2 1927. 6 J. G. MACLAREN POWER CONTROL APPARATUS FOR PNEUMATIC DISPATCH SYSTEMS ay 12. 1926 3 Sheets-Sheet g III/I 7206766072 VWE'ZQ? 0, whv'ero,

I I W April 26. 1927.

1,625,903 J. G. MACLAREN POWER CONTROL APPARATUS FOR PNBUIATIC DISPATCH SYS TEIS Filed lay 12. 1926 3 Sheets-Sheet :5

Patented Apr. 26, 1927.

UNITED STATES PATENT ()FFICE.

JAMES G. MAGLAREN, OF SYRACUSE, NEW YORK, ASSIGNOR TO THE LAMSON COM- PANY, OF SYRACUSE, NEW YORK. A CORPORATION OF MASSACHUSETTS.

POWER-CONTROL APPARATUS FOR PNEUMATIC-DISPATCH SYSTEMS.

Application filed May 12,

This invention pertains to pneumatic dispatch systems of the so-called minimum flow vacuum type and relates more particularly to automatic power controlling apparatus for use in such a system.

Power control apparatus 0t this gene 211 character is disclosed in the patent to Libby No. 968,576, dated August 34), 191.0. The patented apparatus provides automatic pressure actuated means for initiating a carrier impelling air flow through the transmission tube whenever a carrier is entered therein as well as means for cutting oil" such flow after the lapse of a predetermined period o't' time. While I regard the patented device as generally correct in principle and highly eiiective in practice, I believe it preferable to have the cessation of carrier impelling air flow depend directly upon the discharge of the carrier from the delivery end of the tube rather than upon the operation of a timing device, and the principal objectof this invention is to provide an improved power control apparatus comprising means actualole automatically upon insertion of a carrier within the dispatch terminal to initiate flow of the air propelling current and also operating automatically when the last carrier emerges from the delivery terminal to cut oft' the air current abruptly.

In the accompanying drawings. I have illust-rated one preferred emliiodiment ot' the invention by way of example. and in the drawings,

Fig. 1 is a fragmentary elevation. partly in section, illustrating a portion oi the cen tral station desk of a pneunilatic dispatch system having the improved power control apparatus applied thereto;

Fig. 2 is a vertical section to larger scale through the casing of the improved power control apparatus showing the several parts in the position which they occupy when the transmission tube is idle;

Fig. 3 is a view similar to Fig. 2, but showing the parts in the position which they occu y at the instant that carrier impclling air ow is initiated;

Fig. i is a similar 122cm su uring the parts 1926. Serial No. 108,532.

in the position which they occupy during the latter portion of the flight of the carrier through the tube;

Fig. 5 is a similar view, showing the parts in the position which they occupy at the instant after discharge of the last carrier from the tube;

Fig. 6 is a fragmentary section on the line 6 6 of Fig. 7. showing the latch controlling vane within the casing; and

Fig. 7 is a fragmentary front elevation of the casing of the apparatus showing the means tor controlling the vane.

Referring to the drawings, the numeral 1 indicates a fragmentary portion of the central station desk of a pneumatic dispatch system comfnising transmission tubes, such, for example. as the tube 2. which lead from the central station desk to remote sending or clerks stations. Each tube is furnished with a delivery terminal 3, and is provided with a continuation e'l leading to the casing 8 of an individual power control device, in dicated generally by the numeral 5. This power control device is connected by means of a suction tube 7 to a vacuum drum or header 9, in which a low pressure is continually maintained by means of a suitable pump. exhauster, or equivalent apparatus, not shown.

An open-ended dispatch terminal 6 is provided at the central station for each of the transmission stations 2, such dispatch terminal torming the entrance to that run of the tube which leads to the corresponding remote sending station. The above arrangement in general is old and well'known in this art, and further details thereof are, therefore unnecessary, the present invention being directed to improvements in the power control apparatus per se.

Referring more particularly to Figs. 2 to 7, the improved control apparatus as herein disclosed comprises a. hollow casing 8 divided by a partition or septum 10 into an inlet chamber 11 communicating with the tube i and an outlet chamber 12 communicating with the tube 7.

T pi'r'l'o'i to mploy balanced valve Cir for controlling the air flow through the transmission tube I make the partition or septum 10 of substantially tl-shape having the parallel spaced walls 13 and. 1%. These walls are furnished with coaxial valve apertures 15 and 16, respectively, with which cooperate thev heads 17 and 18 of a balanced valve having a stem 19. The valve stem 19 is guided in an opening in a. boss 20 on the upper wall 21 01 the casing 8 and also in a guide opening in the lower end oi? a gland 22 having screw-threaded engagement with an opening ina removable cover plate 23. This cover plate 23 normally closes an opening 2st which gives access to the interior ol? the. casing S and through which the valve heads may be introduced.

A coiled spring sealed within the gland and bears against the lower head 18 of the valve. Th is s nfing tends to close the valve and l'lOlCltllQ heads l7 and 18 in closed position so as suhstantii iliy to cut oil? the flow of air through the transmission tube. The spring may be adjusted by turning the glandQQ.

Preferably the gland is enclosed in a removablecap having an adjustable stop member 27 at its lower end adapted to engage the valve stem 19 and thus to limitthe opening of the valve.

Preferably the valve stem is provided at its up aer part with a stop linger 28 engageable with the ad i'stable stop 29 suitably supported upon the casing and which is adapted to limit the closing movementof the valve. In the preferred mode of use of the apparatus-the adjustable member 29-is so set as to prevent-the valve heads 17 and 18 from closing entirely thus providing for the minimum flow of air which forms a feature of apparatus of this type. While it is preferred to provide the minimum :tlow in this way it is contemplated that it may be obtained in any other usual manner, for enam ile, by providing an opening in septum 10 or by the use of a tube or pipe exterior to the article and leading from the chan'iber ll to the chamber 12.

The upper wall 21 ot the casing proper is provided. with an upstanding' annular flange 30 which cooperates with a hollow cover nicn'iher Sl to term a diaphragm housing. li ithin this housing is arranged a lleuible diaphragm 32- which may hereinafter be referred to under the broad term pneumatic. sincethis diaphragm is regarded as exemplifying any air operated device, for

sample, a piston, bellows, or the like, which responds to variations in pressure. and tlnereb moves a part to'be actuated.

This diaphragm 32 divides its housing into an upper chamber--33 and a lower cham ber The diaphragm 32 is provided at its center with an elongate sleeve 35 telescopinp over the valve stem 19. The lower end o'l this stem is provided with an eulnrn cinent 36 adapted to engage a collar or abutment 37 lined to the valve stem 19 at a point within the chamber The tubular sleeve or stem 35 slides in an opening in a boss 38 in the cover member 31 ot the diaphragm l'iousing. A coiledspring 3i. prcterably otconical shape, so that it may collapse into the smallest possible space is arranged ith-in the chamber-2+1; and bears at one end against the dia 'ihragm and at its other end against the upper surface of the wall Spring 39 thustriuls to raise the diaphragm ito its uppermost position as shown in Figs. 4 and 5.

1e. chamber 34 connnnnicates freely with the inlet chaml; r ll oi the main casing by means oil a constantlyopcn port ltl. Chamber Selcr'ui'ununicates with the chamber 3? by means ot a pfiflfiflf tl all controlled by a needle valve ii 5, the passage l1 normally being oi much less capacity than the port ll].

A port ll}, preferably ot' relativelylarge capacity. as compared with the passage 11, is provided in the cover 31, such port normally being open and permittingatmospheric pressure to act upon the upper side o'lithe diaphragm 32.

An. auxiliary valve 4-4.- is adapted at times to close tlie port ll). This valve 44L is car ricd by a lever pivotally supported. upon a pin 46 carried in spaced brackets mounted upon the cover member 31. a l. pin 4-? projects from the lever Linear its "free end, and one end oi a coiled spring is attached to this pin l7. The other end of this spring is secured in an eye 49 at the lower end of a bracket 50 secured atthe upper end of the valve sten i. The position of the bracket 50 with its eye 4-9 is such that the valve stem moves from its uppermost position. as shown in Fig". 2. to its lowermost position, as shown in 3. the eve 41-9 passes from a point above the plane defined bythe pin 4: and the pivot 46 to a point l'XlOY suchplano and so that in the first position the spring 48 tends to hold the *alve 44: open. while in he second position the spring! tends to hold the valve closed.

The valve stem 19 is turnished with a recess Til. preferably in the term of a groove encircling the storm uni-h re ess normally being: disposed within the boss 0. This h s is tarnished 'ith-a radial opening "for the reception and guidance for one end oi" a sliding}; latch rod 52 whose opposite end is guided in an abutment This latch rod is provided with a collar 54 torn'iine' an abutment for one end of a spring fioencircling the rod. The other end of this spring-bears against the abuti'nent sothat the spring tends to move the latch rod to the 16a viewed in Figs. 2 to The latch rod 0: is provided at its right-hand extremity with a disl; or button 56.

til!

lill

A shaft 57 (Figs. 2, 6 and 7) extends transversely across the inlet end of the cas ing 8, the opposite ends of the shaft being journalled in suitable hearings in the casing, and this shaft carries a vane or battle plate 58 disposed within the entrance of the casing and in the path of the air current flowing through the transmission tube.

The shaft 56 extends beyond one side of the casing and at this side the casing is furnished with a bracket 59 carrying opposed adjustable stop members 60, (31. An arm 62 secured to the upwardly extending end of the shaft 57 plays between the stops and 61, which thus determine or limit the. swinging movement of the vane 58. The arm is furnished with a screw-threaded tail portion 63 for the reception of a nut 64 h avin g one or more apertures for the reception of one end of a spring 65 whose opposite end is secured to a fixed pin 66. This spring tends to hold the arm (52 against the stop (it) so that the vane 58 is normally disposed, as shown in Figs. 2, 3 and 4, with its plane oblique to the air current and with its free edge directed oppositely to the stream of air.

The vane 58 is provided with a pair of upwardly extending fingers 67 spaced to receive the latch rod 52 between them and adapted to engage the button 56 and to move the latch rod to the right when the vane is swung downwardly into the position shown in Fig. 5.

The operation of the device is substantially as follows, it being assumed that the parts are normally positioned as shown in Fig. 2. In this position the port 43 is open, the valve heads 17 and 18 are cutting ofii' carrier impelling air flow through the tube, although a minimum flow is permitted, and the vane 58 is disposed as shown in this figure, while the latch 52 is inoperative, the recess 51 being disposed above the end .of the latch.

\Vhen a carrier is introduced into the transmission tube, either at the open terminal 6 or at the remote sending station. the minimum flow of air through the tube is cut as or substantially reduced so that the pressure in the chamber 34 falls below normal. This decrease is sufficient to permit atmospheric pressure, acting upon the upper side of the diaphragm, to depress the latter in opposition to the action of the spring 39. As the diaphragm 32 moves downwardly, the member 36 forces the abutment collar 3'7 of the valve stem downwardly. compressing the spring 25 and moving the stem 19 and the valve heads 17 and 18 to the full open position shown in Fig. 3. As the stem reaches the lower limit of its movement the recess 51 is brought opposite to the latch 52 and the latter snaps into the recess, thus positively locking the valve in open position. During the downward movement of the valve stem the eye 49 of the bracket 50 passes below the pivot 46 of the lever 45 and the valve it is snapped into closed position, thus cutting off atmospheric pressure from the chamber 33.

The carrier now makes its flight through the tube, since a full carrier impelling air How is permitted through the open valve ports 15 and 16. iLS soon as the valve ports 15 and 16 are opened, a greatly reduced pressure is produced in the chamber 11 and this is immediately transmitted to the cham ber 3-1 through port 10. The air is now gradually sucked out of the closed chamber 33 through the by-pass 41 until the pressure is balanced upon opposite sides of the diaphragm whereupon the spring 39 restores the diaphragm to its uppermost position, as shown in Fig. 1. Since the diaphragm is not positively connected to the alve stem, this upward movement may take place without reference to the position of the valve which ren'lains open and locked during the remainder of the flight of the carrier.

\Vhen the carrier emerges from the tube a sudden rush or gust of air through the tube is produced, and this rush of air, striking the vane 58, swings the latter downwardly in opposition to the spring 55, it being understood that the latter is so tensioned that it holds the vane in the position shown in Fig. 2 in opposition to the normal carrier impelling flow of air which takes place during the flight of the carrier. As the vane 58 swings down in response to the sudden rush of air at the exit of the carrier, the fingers 67 engage the button 56 and retract the latch rod 52 from the recess 51. The spring 2? immediately becomes active to snap the controlling valve into its closed position, and as the valve stem nears its uppermost position the spring 48 again opens the auxiliary valve 44, thus permitting atmospheric pressure to act upon the upper side of the diaphragm. The parts are thus restored to their original position ready for a repetition of the cycle.

In the arrangement thus described the closure of the main valve is dependent solely upon the delivery of the last carrier from the tube. and there is no possibility of partial closure of the main valve prior to such delivery, since the valve is locked in its fully open position during the entire flight of the carrier. and is then closed very abruptly after the carrier has discharged. Such an arrangement is highly advantageous since it ensures a full flow of air during the entire travel of the carrier and is not subject to the so-called wire drawing of the air which takes place in many types of power apparatus, due to gradual, instead of abrupt, closure of the valve.

\Vhile I have illustrated a preferred embodiment of the invention, I wish it to he iii) understood that various changes in proportion otparts, relative positionof: the same, and the substitution of equivalents, may be made Without departing from the spirit of the invention.

I claim;

1. Power control, apparatus for a pneumatie dispatch system of the minimum flow typehaving, a transmission tube, means for creating a carrier propelling air flow there through, and a. controlling valve for govern ing such flow through. ,thetube, a minimum flow being. permitted when the valve is in closed position, said apparatus comprising means for positively holding the valve in fully open position during the flight; of a carrier throughithe tube.

2. Power control v apparatus for a pneumatie dispatch system of the minimum flow typehaving a transmission tube, means for creating a carrier pi 'opelling air flow therethrough, and. a controlling valve c for, governing'jsuch flow through the. tube, a minimum flow being permitted whentl'ie valve is in, closed, position, said apparatus comprising a spring actuatedylatch for holding the, valve in fully open position during the flight of the carrier, through the tube.

8- Power control apparatus of theminimum flow type having. a transmissiontuhe, an exhauster, and a controlling valve for governing carrierimpelling air flow, through the tube, a minimum flow of air through the tube beingrpermitted when the controlling valve is in closed position, said apparatus comprising a pneumatic responding to pressure reduction in the tube due to introduc tion of a carrier therein and by such response openingithe, valve, means tending to close the valve, and means independent of the pneumatict'or holding the valve, in open position so long as a carrier remainsin the tube.

4. Power control apparatus of the minimum flow type having a transmissiontube, an exhauster, and a controlling valve for governing carrier impelling air flow through the tube. a 1n inimum flow-0t air through the tube being pern iitted when the controlling ialve in closed position, said apparatus cmnprising a pneumatic responding to pres sure reductimi in the tube due to introduction of a arrier therein and by such response opening thcvvalve. means for locking the valve in open position, and means independent oi the pneumatic for closing the valve.

5. Power control apparatus of the minimum flow-type having a transmission tube, an eX-hauster, and a controlling valve for governing carrier impelling air flow through the tube, a minimum flow of air through the tube being permitted when the controlling valve is in closed position, saidapparatus cumprising a pneumatic respondingto pressure-reduction inthe tube due to introduction. of a carrier therein and by such response opening the valve, releasable latch means for retaining thevalve in open position, and means for closingthe valve When the latch is released.

6. Power control apparatusof the minimum flow type, having atransmission tube, an exhauster, andv a controlling valve for governin carrier impelling air flow through the tube, aminimnm flow of air through the tube being permitted when the controlling 'alve is in closed position, said apparatus comprising a pneumatic responding to pres: sure reductionin the tube due to introduc tion of a carrier therein and by such ii-espouse opening the valve, releasable locking means for holdingthevalve, open, and means re; sponsive to the delivery of a carrier from the tube to release the, locking, means thereby permitting the valve to close.

7. Power control apparatus of the minimum flow typehavinga transmission tube, an exhauster, and a controllingnvalverfor governing carrier iinpelling airflow through the tube, a minimum flow of air throughthe tube being permitted when. the a controlling valve in closed position, said apparatus comprising a pneumatic respondingto, pressure reauctionin the tube due. to introduction of a carriertherein and by such response openingthevalve, latch means torholding the valve open, and an airuactu ated element for releasing said latch. i

8. Power control. apparatus of theminimum flow type having a transmission tube, an exhauster, and acontrollingvalve for governing carrier impelling air flow through the tube, aminimum flow ojtair throughthe tube beingpermitted when the controlling valve isin closed position, said apparatus comprising a pneumatic responding to pres: sure reduction in the tube due to introduce tion of a carrier therein and by. such response opening the valve, retaining means for .holding the valve in open position, and means iresponsive to the sudden rush of air through the tube, incident, to. delivery of. a carrier therefrom for.releasingthe valve to permit it to close, Y i

9. Power control apparatus cl the minimum flow type having transmission tube, an exhauste and a controlling valve for governingcarrier impelling air flow tl'u'ough the tube, itinlllllll'llllll flow (it-air throughthe tube, being permitted when the controlling, valve is in closed position, said; a niratus comprising a pneumatic responding to pressure reduction in the. tube due to introduction of a carrier therein and bysuch response opening the valve, a retaining latch for holding the, valve inopen position, and an, air actuatedvane moving ,in response to the delivery ota carrier from the tube and byits movement releasing the latch.

1O. Power control apparatusolt the minimum flow type having a transmisison tube, an exhauster, and a controlling valve for governing carrier impelling air flow through the tube, minimum flow of air through the tube being permitted when the controlling valve is in closed position, said apparatus comprising a pneumatic responding to pressure reduction in the tube due to introduction of a carrier therein and by such response opening the valve, a latch for holding the valve in open position, a pivoted vane disposed in the path of the air current passing through the tube, and means normally retaining said vane in inactive position, the vane swinging in response to the sudden rush of air through the tube incident to delivery of a carrier therefrom, and means transmitting movement of the vane to the latch to release the latter and allow the valve to close.

11. Power control apparatus of the minimum flow type having a transmission tube, an exhauster, and a controlling valve for governing carrier impelling air flow through the tube, a minimum flow of air through the tube being permitted when the controlling valve is in closed position, said apparatus comprising a pneumatic responding to pressure reduction in the tube due to introduction of a carrier therein and by such response opening the valve, means independent of the pneumatic for holding the valve in open position, a pivoted vane exposed to the air current flowing in the tube, yielding means normally holding the vane oblique to the air current with its free edge opposed to the current, and means actuable by movement of the vane from normal position to tree the valve from the holding means whereby to permit the valve to close.

12. Power control apparatus of the minimum flow type having a transmission tube, an eXhauSter, and a controlling valve for governing carrier impelling air flow through the tube, a minimum flow of air through the tube being permitted when the controlling valve is in closed position, said apparatus comprising a pneumatic responding to pressure reduction in the tube due to introduction of a carrier therein and by such response opening the valve, a latch for retaining the valve in open position, a pivoted vane exposed to the air current flowing through the tube, stops limiting the are of movement of the vane, yielding means normally holding the vane in inactive position, and a finger carried by the vane adapted to retract the latch and allow the valve to close when the vane swings to abnormal position.

13. Power control apparatus of the minimum flow type having a transmission tube, an exhauster, and a controlling valve for governing carrier impelling air flow through the tube, a minimum flow of air through the tube being permitied when the controlling valve is in closed position, said apparatus comprising a pneumatic responding to pressure reduction in the tube due to introduction of a carrier therein and by such response opening the valve, a spring pressed sliding latch adapted to hold the valve in its open position, a pivoted vane exposed to the air current which flows through the tube, stop means adjustably limiting the are of nuiiveineut ol the vane, a spring normally holding the vane at one limit of its movement, and a linger carried by the vane engaging the lalch to retract the latter and release the valve when the vane swings to abnormal position.

14. Power control apparatus for a pneumatic dispatch system of the minimum flow type having a transmission tube and means for creating a. carrier impelling air flow through the tube, said apparatus comprising a controlling valve for governing such flow, the controlling valve normally cutting off carrier impelling air flow, a minimum flow through the tube normally being permitted, a pneumatic which advances in response to decrease in pressure in the tube due to introduction of a carrier therein and thereby opens the valve, locking means independent of the pneumatic ior positively holding the valve open during the flight of the carrier, and means for abruptly releasing the looking means when the carrier is delivered from the tube.

15. Power control apparatus for a pneumatic dispatch system of the minimum flow type having a transmission tube and means [or creating a carrier impelling air flow through the tube, said apparatus comprising a controlling valve for governing such flow, the controlling valve normally cutting ofi' carrier impelling air flow, a minimum flow through the tube normally being permitted, a pneumatic which advances in response to decrease in pressure in the tube due to introduction of a carrier therein and thereby opens the valve, means causing the pneumatic to retreat substantially to normal position during flight of the carrier, and positive means for holding the valve in fully open position during the flight of the Cflll'lGI'.

16. Power control apparatus for a pneumatic dispatch system of the minimum flow type having a transmission tube and means for creating a carrier impelling air flow through the tube, said apparatus comprising a controllng valve for governing such flow, the controlling valve normally cutting otl' carrier impelling air flow, a minimum flow through the tube normally being permitted, a pneumatic which advances in response to decrease in pressure in the tube due to introduction ot a carrier therein and thereby opens the valve, means causing the pneumatic to retreat substantially to normal position during flight of the carrier, means independent of the pneun'iatic for closing the valve, and latch means retaining the valve in fully open position until the carrier is delivered from the tube.

17. Power control apparatus for a pneumatic dispatch system of the minimum flow type having a transmission tube and means for creating a carrier impelling air flow through the tube, said apparatus comprising a' controlling valve for governing such flow, the controlling valve normally cutting oil carrier impelling air flow, a minimum flow through the tube'normally being permitted, a pneumatic Which advances in response to decrease in pressure in the tube due to introduction of a carrier therein and thereby opens the valve, a spring adapted to restore the pneumaticsubstantially to normal position' during the flight of the carrier, latch for holding the valve open during the flight of the carrier, a spring for closing the valve, and means-tor releasing the latch to permit the valve to closeWhen the carrier is delivered from the tube.

18 Povver control apparatustor a pneumaticdis'patchfsystem of the minimum flow type having a transmission tube and an exhauster, said apparatus comprising a controllingvalve for governing carrier impel ling air flowthr'ough the tube, a minimum flow of air being permitted When the controlling valve is in closed position, a pneumatic'which moves in one direction in re sponse to introduction of a carrier into the tubeand thereby opens the controlling valve, the pneumatic being free to return to normal'position, independently of the valve, a

spring tending to close the valve, and means tor holding the valve open during the fh ant of the carrier and for abruptly releasing the valve toalloW it to close when the carrier is delivered from the tube.

'194'P0vver control apparatus for a pneumatic dispatch system 01 the vacuum mini- I! t1 1 1 mum flow type having a transmission tube, means for creating a carrier propelling; air

flotvther'ethrough, a controlling valve for governing such flow through the tube, a

"inin'imiin'i flow being permitted when the valve is in closed position, and means for opening thevalve and positively holdlng it in fully open position during the Eight of the carrier through the tube and for permit ting the valve to close abruptly from its fully open position when the carrier is de- "livered from the tube.

governing such flow through the tube, a

mn'iinium flow being permittedwhen the valve is in closed position, means for opening the valve, independent means for hold ing the valve in fully open position during the entire flight oi the carrier, and means for abruptly closing the valve when the carrier emerges from the tube.

21. Power control apparatus for a pneumatic dispatch system 01 the vacuum mini.- mum liow type having a transmission tube, means for creating a carrier propelling air flow therethrough, a controlling valve for governing such. flow through the tube, a minimum flow being permitted When the valve is in closed position, means for opening' the valve when a carrier *is introduced into'the tube, latch means for holclling the valve Wide open so longlas'thejcarrier remains in thetu'be, means forclo'singthe valve abruptly from its "wide open position when the latch is releasech'and means acting automatically when the carrier leaves "the tube for releasing the latch.

22. Power control apparatus for ap'neumatic dispatch system of the minimum'flow type having a transmission tube and" an exhaust-er, said apparatus comprisinga com trolling valve for governing carrien impelling air :tlowthrough the tube, a minimum new of air through the tube being permitted w'hen the controlling valve isincloed position, areciprocating stem for the controlling valve, an abutment hired to "the stem, a pneumatic having a part'engageable with said abutment'the'reby to open the valve as the pneumatic moves in"onedirection, the pneumatic moving independently of i the valve in the opposite direction, a latch for holding the valve in open position, and means for closing the valve When theltxtch is released.

23. Power control apparatus "for a pneumatic dispatchsystem of the minimum flow type having a transmission tube and an exhauster, said apparatus comprising a controlling valve torgoverning ca irier iinpeL ling air flow through the tube, aminiinum flow otair through tl'ie'tube being permitted when the controlling valveis in clos'ed position, a reciprocating stcm for the controlling valve, an abutment lined to the steinja pneumatic provided tvith a tubular stem sliding upon the valvestem and en'gagcable With the abutment as thepneumatic moves in one direction thereby to open the valve, and a latch engageable with arec'ess in the valve stem to hold the valve open.

24. Power control apparatus for a pneumatic dispatch system of the minimum flow type having a transmission tube, means for creating a carrier propelling air 'flovv therethrough, and a controlling valve for governing such flow through the tube, a minimum flow being permitted when the valve is in closed position, said apparatus con1- prising latch means for holding the valve for closing the auxiliary valve, and means open, a spring tending to close the valve, a permitting equalization of pressure upon 0ppneumatic for opening the valve, one side posite sides of the pneumatic when the auxof the pneumatic normally being exposed to iliary valve is closed.

5 atmospheric pressure, an auxiliary valve for Signed by me at Syracuse, New York, this cutting off atmospheric pressure from the 8th day of May, 1926. pneumatic, means actuated by the pneumatic JAMES G. MAGLAREN. 

